Wellbores may be drilled into a surface location or seabed for a variety of exploratory or extraction purposes. For example, a wellbore may be drilled to access fluids, such as liquid and gaseous hydrocarbons, stored in subterranean formations and to extract the fluids from the formations. A variety of drilling methods and tools may be utilized depending partly on the characteristics of the formation through which the wellbore is drilled.
A drilling system may use a variety of bits in the creation, maintenance, extension, and abandonment of a wellbore. Bits include drilling bits, mills, reamers, hole openers, and other cutting tools. Some drilling systems rotate a bit relative to the wellbore to remove material from the sides and/or bottom of the wellbore. Some bits are used to remove natural material from the surrounding geologic formation to extend or expand the wellbore. For instance, so-called fixed cutter or drag bits, or roller cone bits, may be used to drill or extend a wellbore, and a reamer or hole opener may be used to remove formation materials to extend or widen a wellbore. Some bits are used to remove material positioned in the wellbore during construction or maintenance of the wellbore. For example, bits are used to remove cement, scale, or metal casing from a wellbore during maintenance, creation of a window for lateral drilling in an existing wellbore, or during remediation.
Bit bodies may be fabricated from either steel or a hard metal “matrix” material. The matrix material can include tungsten carbide infiltrated with a binder alloy. Matrix bit bodies may have higher wear or erosion resistance, but may sacrifice toughness and may be more susceptible to impact damage than steel bit bodies.
Matrix bit bodies are manufactured by sintering, a process unique from infiltration. The sintering process involves the introduction of a refractory compound into a mold. The refractory may include a carbide of tungsten, titanium, or tantalum, or other specialized use materials. Before the carbide is introduced into the mold, it is mixed with a binder metal. The binder metal may be cobalt, but iron, nickel, and other materials may also be used. In the mold, the combination is heated to a point just below the melting point of the binder metal, and bonds are formed between the binder metal and the carbide by diffusion bonding or by liquid phase material transport.
Infiltration, on the other hand, involves the introduction of a refractory compound such as the above carbides into a mold with an opening at its top. A slug or cubes of binder metal are then placed against the refractory compound at the opening. The mold, refractory compound, and binder metal are placed into a furnace, and the binder metal is heated to its melting point. By capillary action and gravity, the molten metal from the slug infiltrates the refractory compound in the mold, thereby binding the refractory compound into a part. The infiltration binder may be a copper alloy including nickel, manganese, zinc, tin, other materials, or some combination thereof.
Cutting elements on a bit may be formed of an ultrahard material, such as a tungsten carbide or polycrystalline diamond (PCD). PCD may be used in various drilling operations as the material is very hard and wear resistant. PCD is, however, susceptible to thermal degradation during operations.